KR20060130551A - Low carbon alloy steel tube having ultra high strength and excellent toughness at low temperature and method of manufacturing the same - Google Patents

Abstract

A low carbon alloy steel tube and a method of manufacturing the same, in which the steel tube consists essentially of, by weight: about 0.06% to about 0.18% carbon; about 0.5% to about 1.5% manganese; about 0.1% to about 0.5% silicon; up to about 0.015% sulfur; up to about 0.025% phosphorous; up to about 0.50% nickel; about 0.1% to about 1.0% chromium; about 0.1% to about 1.0% molybdenum; about 0.01% to about 0.10% vanadium; about 0.01% to about 0.10% titanium; about 0.05% to about 0.35% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities. The steel has a tensile strength of at least about 145 ksi and exhibits ductile behavior at temperatures as low as -60 °C.

Description

LOW CARBON ALLOY STEEL TUBE HAVING ULTRA HIGH STRENGTH AND EXCELLENT TOUGHNESS AT LOW TEMPERATURE AND METHOD OF MANUFACTURING THE SAME}

This application is directed to US Provisional Application No. 60 / 509,806, filed Oct. 10, 2003, and US Non-Provisional Application No., filed October 5, 2004. Insist on the benefits.

The present invention relates to low carbon alloy steel tubes having ultra high strength and good toughness at low temperatures and also to methods of making such steel tubes. Steel Tube Paper Car Particularly suitable for manufacturing parts for containers for system parts, for example an automobile airbag inflator.

Airbag inflators for vehicle passenger restraint systems are needed to meet stringent structural and functional criteria. Therefore, strict procedures and patience are imposed on the manufacturing process. Field experience indicates that the industry has been successful in meeting past structural and functional criteria, while at the same time a continuous reduction in manufacturing costs is also important, but improved and / or new features are needed to meet the evolving requirements.

Airbags or supplemental papermaking systems are important safety features in many vehicles today. In the past, airbag systems were of the type that used explosive chemicals, but because of their high cost and environmental and recycling concerns, in recent years, newer use of accumulators made of steel tubes filled with argon gas or the like One type of inflator has been developed, and this type is increasingly used.

The accumulators mentioned above are containers which normally hold high pressure gas or the like which is blown into the airbag in a single or multiple stage burst in the event of a motor vehicle crash. Thus, steel tubes used as such accumulators must be pressurized at high strain rates in a very short period of time. Thus, compared with simple structures such as ordinary pressure cylinders, the above-mentioned steel tube has excellent dimensional accuracy, workability, And weldability and it should also have high strength, toughness, and good resistance to bursting. Dimensional accuracy is important to ensure a very accurate volume of gas blown into the airbag.

Cold forming features are very important for the members of the tube used to make the accumulator because they are molded into the final shape after the seamless tubes have been manufactured. Other shapes depending on the container arrangement will be obtained by cold forming. It is important to obtain a pressure vessel free from cracks and surface defects after cold forming. Moreover, it is extremely important to have very good toughness even at low temperatures after cold forming.

The developed steel has very good weldability, and no preheating or postwelding heat treatment is required for the present application. Equivalent, as defined by the formula

Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15

It should be less than about 0.63% to obtain the required weldability. In a preferred embodiment of the present invention, the carbon equivalent as defined above should be less than about 0.60% to better guarantee weldability.

To produce a gas container, cold - drawn tubes made in accordance with the present invention are cut to length and then cold formed using other known techniques (crimping, swaging, or the like). Alternatively, welded tubes could be used. Then, to manufacture the accumulators, end caps and diffusers were welded to each end of the vessel by appropriate techniques such as friction welding, gas tungsten arc welding or laser welding. Such welding is very important and in itself requires testing to ensure weld integrity through considerable labor and, in some cases, pressure vessel and airbag deployment. It has been observed that these welds can crack or fail, thus jeopardizing the accumulator integrity and possibly the operation of the airbag.

Inflators are tested to ensure that they maintain their structural integrity during airbag deployment. One such test is the so-called burst test. This is a fracture-type test where the canister is subjected to normal operating use, ie, significantly higher internal pressure than expected during airbag deployment. In this test, the inflator is subjected to increased internal pressure until rupture occurs.

In reviewing the rupture test and studying the test canister specimens from these tests, it has been found that fracture occurs through other optional methods: ductile fracture , brittle fracture, and sometimes a combination of these two approaches. It has been observed that in ductile fracture occurs an outturned rupture exemplified by an open bulge (as indicated by the bursting bubbles). The ruptured surface is inclined approximately 45 degrees with respect to the tube outer surface and is localized within the subject area. In brittle fracture, on the other hand, non-arresting longitudinal cracks appear along the length of the inflator, which indicates brittle zones in the material. In this case, the fracture surface is common to the tube outer surface. Both modes of breakage have a unique surface when viewed under a scanning electron microscope-although cracking is a sign of brittleness, dimples are characteristic of ductile breakdown.

Sometimes a combination of these two modes of failure can be observed and brittle cracks can propagate out of the soft, ruptured areas. Since the entire system including the airbag inflator can be used in vehicles operating in very different climates, it is important that the material exhibits ductile behavior over a wide temperature range, from very cold to hot temperatures.

Summary of the invention

The present invention relates to low carbon alloy steel tubes suitable for cold forming with very high strength (minimum UTS 145 ksi) and, as a result, very high burst pressures. Moreover, steel has good toughness at low temperatures, and has a ductile behavior that is guaranteed at temperatures as low as -60 ° C., ductile-brittle transition temperature (DBTT), and possibly even as low as -100 ° C. The invention also relates to a method for producing such a steel tube.

The material of the present invention is designed to make parts for containers for automotive papermaking system parts, for example an automotive airbag inflator.

While the present invention may take embodiments in many forms, it is to be understood that the presently preferred embodiments are hereafter described with the understanding that they are not intended to limit the invention to the specific embodiments considered and described as illustrative of the invention. Will be.

The present invention relates to steel tubing used in stored gas expander pressure vessels. More specifically, the present invention is directed to low carbon, ultra high strength steel grades for seamless pressure vessel applications with guaranteed ductile behavior at -60 ° C, ie, ductile-brittle transition temperatures below -60 ° C. It is about.

More specifically, the present invention relates to a manufacturing method for obtaining a seamless steel tube used for making chemical compositions and expanders.

A schematic description of a method of making a seamless low carbon ultra high strength steel is as follows.

1. Manufacture of steel

2. steel casting

3. Tue hot rolling

4. Hot Rolled Hollow Finish

5. Cold Drawn

6. Heat treatment

7. Cold-drawn tube finishing work

One of the main purposes of the steel-making process is to refine iron by removal of carbon, silicon, sulfur, phosphorus, and manganese. In particular, sulfur and phosphorus are disadvantageous for steel because they deteriorate the mechanical properties of the material. Ladle metallurgy is used before or after foundation treatment to perform certain purification steps that allow for faster treatment in foundation steel fabrication operations.

The steel-making process is carried out under extreme clean run to obtain very low sulfur and phosphorus contents, which in turn are important to obtain the high toughness required by the product. Therefore, the purpose of inclusions of -thin series below level 2 or below 2 and -heavy series below level 1 or below under the guidance of ASTM E45-Worst Field Method (Method A). Was imposed. In a preferred embodiment of the present invention, the maximum microencapsulation content should be as shown in the table below, as measured according to the criteria mentioned above.

Moreover, extreme clean runs allow obtaining oversize inclusion contents with 30 μm or less in size. This inclusion body content is obtained while limiting the total oxygen content to 20 ppm.

Extreme clean run in secondary metallurgy is performed by bubbling an inert gas in a ladle furnace to support inclusion bodies and impurities. The generation of fluid slag that can absorb impurities and inclusions, and the size and shape change of inclusions by addition of SiCa to liquid steel, results in high quality steels with low inclusion content.

The chemical composition of the steel obtained will be as follows. In each case "%" means "mass percent":

Carbon (C)

C is an element which raises the strength of steel at low cost, but if its content is less than 0.06%, it is difficult to obtain the desired strength. On the other hand, if the steel has a C content in excess of 0.18%, then cold workability, weldability, and toughness decrease. Therefore, the C content ranges from 0.06% to 0.18%. The preferred range of C content is 0.07% to 0.12%, and even more preferred ranges are 0.08% to 0.11%.

Manganese (Mn)

Mn is an effective element for increasing the hardenability of steel, and therefore it increases strength and toughness. If its content is less than 0.5%, it is difficult to obtain the desired strength, whereas if it exceeds 1.5%, then a banding structure remains, and the toughness decreases. Therefore, Mn content is 0.5%-1.5%. However, the preferred Mn range is 1.00% to 1.40%, more preferably 1.03% to 1.18%.

Silicon (Si)

Si is an element having a deoxygenation effect during the steel fabrication process and also increases the strength of the steel. If the Si content is less than 0.10%, the steel is susceptible to oxidation, while if it exceeds 0.50%, then both the toughness and workability decrease. Therefore, Si content is 0.1%-0.5%. Preferable Si ranges are 0.15%-0.35%.

Sulfur (S)

S is an element causing the reduction of toughness of steel. Thus, the S content is limited to at most 0.015%. Preferred maximums are 0.010% and more preferred maximums are 0.003%.

Phosphorus (P)

P is an element causing the reduction of toughness of steel. Thus, the P content is limited to a maximum of 0.025%. Preferred maximum is 0.015%, more preferred maximum is 0.012%.

Nickel (Ni)

Ni is an element that increases the strength and toughness of steel, but it is very expensive, so Ni is limited to a maximum of 0.50%. Preferred maximums are 0.20% and more preferred maximums are 0.10%.

Chrome (Cr)

Cr is an effective element for increasing the strength, toughness, and corrosion resistance of steel. If its content is less than 0.10%, it is difficult to obtain the desired strength. On the other hand, if it exceeds 1.0%, then the toughness in the weld zone is significantly reduced. Therefore, Cr content is 0.1%-1.0%. However, the preferred Cr range is 0.55 to 0.80%, more preferably 0.63% to 0.73%.

Molybdenum (Mo)

Mo is an effective element for increasing the strength of steel and contributes to retarding softening during tempering. If its content is less than 0.10%, it is difficult to obtain the desired strength, whereas if it exceeds 1.0%, then the toughness in the welding zone is significantly reduced. Therefore, the Mo content is 0.1% to 1.0%, but this iron alloy is expensive and there is a need to lower the maximum content. Therefore, the preferred Mo range is 0.30% to 0.50%, more preferably 0.40% to 0.45%.

Vanadium (V)

V is an effective element to increase the strength of steel, even in small amounts, and allows to delay softening during tempering. The V content is found to be optimal at 0.01% to 0.1%. However, this ferroalloy is expensive and needs to be lowered to its maximum content. Therefore, the preferred V range is 0.01% to 0.05%, and more preferably 0.03% to 0.05%.

Titanium (Ti)

Ti, even when added in small amounts, is an effective element for increasing the strength of steel. It is found that the Ti content is optimally 0.01% to 0.1%. However, this ferroalloy is expensive and needs to be lowered to its maximum content. Therefore, the preferred Ti range is 0.01% to 0.05%, and more preferably 0.025% to 0.035%.

Copper (Cu)

This element improves the corrosion resistance of the pipe, therefore the Cu content is in the range of 0.05% to 0.35% and more preferably in the range of 0.15% to 0.30%.

Aluminum (Al)

This element is added to the steel during the steel fabrication process to reduce the inclusion content and to refine the steel grains. Preferred Al content is in the range of 0.010% to 0.050%

Preferred ranges of other elements not described above are as follows:

element weight

Niobium up to 0.05%

Sn max 0.05%

Sb up to 0.05%

Pb up to 0.05%

As max 0.05%

Residual elements in a single ladle of steel used to make tubes or chambers would be as follows:

Sn + Sb + Pb + As ≤ 0.15% at maximum, and

S + P ≦ 0.025.

The next step is steel casting to produce solid steel rods that can be drilled and rolled to form seamless steel tubes. The steel is cast into round solid steel slabs in a steel mill and has a uniform diameter along the steel axis.

Solid cylindrical steel pieces of ultra-clean steel are heated to a temperature of about 1200 ° C to 1300 ° C and subjected to rolling mill treatment at this temperature. Preferably, the slabs are heated to a temperature of about 1250 ° C. and then passed through a rolling mill. Preferably, using the known Manessmann treatment, the steel piece is drilled, after which its length increases significantly during hot rolling, while the outer diameter and wall thickness are significantly reduced. For example, a 148 mm outer diameter solid rod is hot rolled into a 48.3 mm outer diameter hot rolled tube with a wall thickness of 3.25 mm.

The cross section reduction, measured as the ratio of the cross section of the solid slabs to the cross section of the hot rolled tube, is important for obtaining the refined microstructure necessary to achieve the desired mechanical properties. Therefore, the minimum cross-sectional area reduction is 15: 1, each with a minimum cross-sectional area reduction of preferably 20: 1 and most preferably 25: 1.

The seamless hot rolled tube of ultra-clean steel thus produced is cooled to room temperature. The seamless hot rolled tubes of the ultra high clean steel thus produced have approximately uniform wall thickness, both circumferentially around both tubes and in length along the tube axis.

The hot rolled tube then passes through another finishing step, such as, for example, cut into lengths of 2-4 pieces, the ends of which are cut and, if necessary, calibrated with known rotary straightening devices, and subjected to electromagnetic or ultrasonic testing. It is tested non-destructively by one or more other known techniques, such as

The surface of each piece of hot rolled tube is then conditioned appropriately for cold drawing. This conditioning includes pickling by dipping into the acid solution and applying a suitable layer of lubricant, such as a known zinc phosphate and sodium esterate combination, or reaction oil. After surface conditioning the seamless tube is cold drawn and pulled through an outer die having a diameter smaller than the outer diameter of the drawn tube. In most cases, the inner surface of the tube is also supported by an inner mandrel fixed to one end of the rod such that the mandrel stays close to the die during drawing. This drawing operation is carried out without the need to preheat the tube above room temperature.

The seamless tube is so cold drawn at least once, and each pass reduces both the outer diameter and the wall thickness of the tube. The cold-drawn steel tube so produced has a uniform outer diameter along the tube axis, and has a uniform wall thickness both in the circumference of the tube and in length along the tube axis. Such cold-drawn tubes preferably have an outer diameter of 10 to 70 mm, and preferably a wall thickness of 1 to 4 mm.

The cold-drawn tube is then at least the upper austenitizing temperature, or Ac3 (which is about 880 ° C. for the particular chemistry disclosed herein), but preferably above about 920 ° C. in the austenitic furnace and Heat treatment to a temperature below about 1050 ° C. This maximum austenitization temperature is imposed to avoid particle coarsening. This treatment can be carried out in a fuel furnace or an induction furnace, but preferably in the latter. The speed of transition in the furnace is strongly dependent on the type of furnace used. It has been found that the high surface quality required by this application is better obtained if an induction furnace is used. This is due to the nature of the induction treatment, which involves a very short transition time which prevents oxidation from occurring. Preferably, the austenitization heating rate is at least about 100 ° C. per second, but more preferably at least about 200 ° C. per second. Extremely high heating rates and, as a result, very low heating times are important for obtaining very good particle microstructures and in turn guarantee the required mechanical properties.

Moreover, a suitable filling factor, defined as the ratio of the rounded area defined by the outer diameter of the tube to the rounded area defined by the coil inner diameter of the induction furnace, is important for obtaining the required high heating rate. The minimum fill factor is about 0.16 and the preferred minimum fill factor is about 0.36.

At or near the outlet zone of the furnace the tube is quenched by a suitable quenching fluid. The quenching fluid is preferably water or a water-based quenching solution. The tube temperature drops rapidly to ambient temperature, preferably at a rate of at least about 100 ° C. per second, more preferably at a rate of at least about 200 ° C. per second. This extremely high cooling rate is important for obtaining complete microstructure deformation.

The steel tube is then tempered at a temperature below Ac1 with appropriate temperature and circulation time. Preferably, the tempering temperature is about 400-600 ° C. and more preferably about 450-550 ° C. The immersion time will be long enough to ensure very good temperature homogeneity, but if it is too long, the desired mechanical properties are not obtained. Thus, a soak time of about 2-30 minutes, preferably about 4-20 minutes, was used. The tempering treatment is preferably carried out in a neutral atmosphere to reduce the protection or to avoid decarbonization and oxidation of the tubes.

The ultra high strength steel tubes thus produced are passed through different finishing stages, calibrated in known rotary straightening devices and tested non-destructively by one or more known techniques. Preferably, for this kind of application the tube should be tested by both known ultrasonic and electromagnetic techniques.

After the heat treatment, the tubes can be chemically treated to obtain tubes with the desired appearance and very low surface roughness. For example, the tube could be pickled in sulfuric acid and hydrochloric acid solution, phosphorylated with zinc phosphate and oiled with petroleum-based oil, water-based oil, or mineral oil.

The steel tube obtained by the described method will have the following mechanical properties to comply with the requirements stated for the present invention.

Yield strength minimum about 125 ksi (862 MPa)

More preferably at least 135 ksi (930 Mpa)

Seal Minimum strength of about 145 ksi (1000 MPa)

Elongation At least about 9%

Hardness up to approximately 40 HRC

More preferably up to 37 HRC

surrender Strength, tensile strength, elongation, and hardness The test will be performed according to the procedures described in standards ASTM E8 and ASTM A370. For the tensile test, full size specimens for evaluating the entire tube portion are preferred.

The straightening test will be in accordance with clause 178.65, Specification Dot 39 in 49 CFR. Thus, the tube portion will not crack when flattened with a V-shaped tool angled at 60 degrees, until the opposite side drops to six times the tube wall thickness. This is fully met by the developed steel.

In order to obtain a good balance between strength and toughness, the former (sometimes called electron) austenite particle size is preferably 7 or finer and more preferably 9 or more, as measured according to ASTM E-112 standard. Will be fine. This is achieved thanks to extremely short thermal cycling during austenite treatment.

The steel tube obtained by the described method will have the stated properties to comply with the requirements stated for the present invention.

The demand in the art continues to impose roughness requirements to lower value. The present invention has a good visual appearance with the surface finish of closed tubes up to 3.2 microns, for example, on both the outer and inner surfaces. This requirement is achieved through cold drawing, short austenitization time, reduced or neutral atmospheric tempering, and appropriate surface chemical conditioning at different stages of treatment.

The hydroburst pressure test will be performed by sealing the end of the tube portion, such as by welding a flat plate to the end of the tube. Complete hoop stress It is important that the 300 mm tube section remain constraint free so that it can be developed.

Pressurization of the tube portion may be carried out by pumping oil, water, alcohol or mixtures thereof.

Burst test pressure requirements depend on tube size. When rupture is tested, the ultra high strength steel seamless tube has a ductile behavior that is guaranteed at -60 ° C. Tests performed on the resulting samples show that this grade has a ductile-brittle transition temperature of less than -60 ° C, with guaranteed ductile behavior at -60 ° C.

The inventors found that, instead of the Charpy impact test (according to ASTM E23), a far more representative verification test is the burst test, which is carried out at ambient and low temperatures. This is due to the fact that relatively thin wall thicknesses and small outer diameters are used in these products and therefore the reference ASTM specimens for the Charpy impact test cannot be standardized from the tube in the transverse direction. Moreover, in order to obtain such a subsized Charpy impact probe, a straightening strain must be applied to the curved tube probe. This has a sensitive effect on steel mechanical properties, especially at certain impact strengths. Therefore, a representative impact test is not obtained with this procedure.

Claims (39)

About 0.06% to about 0.18% carbon by weight; About 0.5% to about 1.5% manganese; About 0.1% to about 0.5% silicon; Up to about 0.015% sulfur; Up to about 0.025% phosphorus; Up to about 0.50 nickel; About 0.1% to about 1.0% chromium; About 0.1% to about 1.0% molybdenum; About 0.01% to about 0.10% vanadium; About 0.01% to about 0.10% titanium; About 0.05% to about 0.35% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And a low carbon alloy steel tube consisting essentially of balance iron and incidental impurities, wherein the steel tube has a tensile strength of at least about 145 ksi and has a ductile-brittle transition temperature of less than -60 °. The method of claim 1, wherein the steel tube is weight percent, from about 0.07% to about 0.12% carbon; About 1.00% to about 1.40% manganese; About 0.15% to about 0.35% silicon; Up to about 0.010% sulfur; Up to about 0.015% phosphorus; Up to about 0.20 nickel; About 0.55% to about 0.80% chromium; About 0.30% to about 0.50% molybdenum; About 0.01% to about 0.07% vanadium; About 0.01% to about 0.05% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And low carbon alloy steel tubes consisting essentially of balanced iron and incidental impurities. The method of claim 1, wherein the steel tube is weight percent, from about 0.08% to about 0.11% carbon; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; Up to about 0.10 nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; About 0.03% to about 0.05% vanadium; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And low carbon alloy steel tubes consisting essentially of balanced iron and incidental impurities. The low carbon alloy steel tube of claim 1, wherein the steel tube has a yield strength of at least about 125 ksi. The low carbon alloy steel tube of claim 1, wherein the steel tube has a yield strength of at least about 135 ksi. The low carbon alloy steel tube of claim 1, wherein the steel tube has an elongation at break of at least about 9%. The low carbon alloy steel tube of claim 1, wherein the steel tube has a hardness of about 40 HRC or less. The low carbon alloy steel tube of claim 1, wherein the steel tube has a hardness of about 37 HRC or less. The low carbon alloy steel tube of claim 1, wherein the steel tube has a carbon equivalent of less than about 0.63 and the carbon equivalent is determined according to the following formula: Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15 10. The low carbon alloy steel tube of claim 9, wherein the steel tube has a carbon equivalent of less than about 0.60%. 10. The low carbon alloy steel tube of claim 9, wherein the steel tube has less than about 0.56% carbon equivalent. The steel tube of claim 1, wherein the steel tube is of a less than 2 or 2 foil series and a level 1 or less than 1 medium, as measured according to ASTM E45. A low carbon alloy steel tube having a maximum microinclusion content. The low carbon alloy steel tube of claim 1, wherein the steel tube has a maximum microencapsulation content measured according to ASTM E45 standard—Worst Field Method (Method A):

14. The low carbon alloy steel tube of claim 13, wherein an oversize enclosure content having a size of 30 μm or less is obtained. 15. The low carbon alloy steel tube of claim 14, wherein the total oxygen content is limited to 20 ppm. The low carbon alloy steel tube of claim 1, wherein the tube has a seamless structural arrangement. A stored gas expander pressure vessel comprising the low carbon alloy steel tube of claim 1. Automobile airbag inflator comprising the low carbon alloy steel tube of claim 1 About 0.08% to about 0.11% carbon by weight; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; Up to about 0.10 nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; About 0.03% to about 0.05% vanadium; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And a low carbon alloy steel tube consisting essentially of balance iron and incidental impurities, wherein the steel tube has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least about 9%, a hardness of about 37 HRC or less, and Low carbon alloy steel tubes having a ductile-brittle transition temperature of less than -60 ° C. 20. The low carbon alloy steel tube of claim 19, wherein the tube is in a seamless structural arrangement. 20. A stored gas expander pressure vessel comprising the low carbon alloy steel tube of claim 19. 20. An automotive airbag inflator comprising the low carbon alloy steel tube of claim 19. A method of making a length steel tubing for a stored gas expander pressure vessel, the method comprising the following steps: About 0.06% to about 0.18% carbon by weight; About 0.5% to about 1.5% manganese; About 0.1% to about 0.5% silicon; Up to about 0.015% sulfur; Up to about 0.025% phosphorus; Up to about 0.50 nickel; About 0.1% to about 1.0% chromium; About 0.1% to about 1.0% molybdenum; About 0.01% to about 0.10% vanadium; About 0.01% to about 0.10% titanium; About 0.05% to about 0.35% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And producing a length of tubing from a steel material consisting essentially of balance iron and incidental impurities; Cold-drawing the steel tube to obtain the desired dimensions; Austenitizing by heating a cold-drawn steel tube in an induction-type austenitizing furnace at a heating rate of at least about 100 ° C. per second to a temperature of Ac 3 or higher; After the heating step, quenching the steel tube in the quenching fluid until the steel tube reaches approximately ambient temperature at a cooling rate of at least about 100 ° C. per second; And After the quenching step, tempering the steel tube at a temperature below Ac1 for about 2-30 minutes. 24. The steel tube of claim 23 wherein the steel tube produced is weight percent, from about 0.07% to about 0.12% carbon; About 1.00% to about 1.40% manganese; About 0.15% to about 0.35% silicon; Up to about 0.010% sulfur; Up to about 0.015% phosphorus; Up to about 0.20 nickel; About 0.55% to about 0.80% chromium; About 0.30% to about 0.50% molybdenum; About 0.01% to about 0.07% vanadium; About 0.01% to about 0.05% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And balance iron and incidental impurities. 24. The steel tube of claim 23 wherein the steel tube produced comprises about 0.08% to about 0.11% carbon by weight; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; Up to about 0.10 nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; About 0.03% to about 0.05% vanadium; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And balance iron and incidental impurities. The method of claim 23, wherein the finished steel tube has a yield strength of at least about 125 ksi. The method of claim 23, wherein the finished steel tube has a yield strength of at least about 135 ksi. The method of claim 23, wherein the finished steel tube has a yield strength of at least about 145 ksi. The method of claim 23, wherein the finished steel tube has an elongation at break of at least about 9%. The method of claim 23, wherein the finished steel tube has a hardness of about 40 HRC or less. The method of claim 23, wherein the finished steel tube has a hardness of about 37 HRC or less. The method of claim 23, wherein the finished steel tube has a ductile-brittle transition temperature of only less than -60 ° C. 24. The method of claim 23, wherein in the austenitized heating step, the steel tube is heated to a temperature of about 920-1050 ° C. The method of claim 23, wherein in the austenitized heating step, the steel tube is heated at a rate of at least about 200 ° C. per second. The method of claim 23, wherein in the quenching step, the steel tube is cooled at a rate of at least about 200 ° C. per second. The method of claim 23, wherein in the tempering step, the steel tube is tempered to a temperature of about 400-600 ° C. 25. The method of claim 36, wherein in the tempering step, the steel tube is tempered for about 4-20 minutes. The method of claim 23, wherein the tempered steel tube further comprises a finishing step of pickled, phosphorylated and oiled. A method of manufacturing a length of steel tube for a stored gas inflator pressure vessel, About 0.08% to about 0.11% carbon by weight; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; Up to about 0.10 nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; About 0.03% to about 0.05% vanadium; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15% residual element; And producing a length of tube from a steel material consisting essentially of balance iron and incidental impurities; Cold-drawn to steel tube to obtain desired dimensions step; Austenitizing by heating a cold-drawn steel tube in an induction-type austenitic furnace at a temperature of about 920-1050 ° C., at a heating rate of about 200 ° C. or more per second; After the heating step, quenching the steel tube with a water-based quenching solution until the tube reaches approximately ambient temperature at a cooling rate of at least about 200 ° C. per second; And After the quenching step, tempering the steel tube at a temperature of about 450-550 ° C. for about 4-20 minutes, A tempered steel tube includes a finishing step of pickling, phosphorylating and lubricating, Wherein the finished steel tube has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least about 9%, a hardness of about 37 HRC or less, and a ductile-brittle transition temperature below -60 ° C. Manufacturing method.